I. Field of the Invention
The present invention relates to a cold start fuel control system for an internal combustion engine.
II. Description of Related Art
Most modern day internal combustion engines of the type used in automotive vehicles include a plurality of internal combustion chambers. A primary intake manifold has one end open to ambient air and its other end open to the combustion chambers through intake ports formed in the engine housing as well as through one or more engine intake valves associated with each combustion chamber.
In order to provide fuel to the engine, a multi-point fuel injector is associated with each of the internal combustion engine chambers. During a warm engine operating condition, the multi-point fuel injectors, under control from the electronic control unit for the engine, provide fuel to the engine. The electronic control unit ideally controls the amount of fuel provided to the engine to achieve the desired engine performance while minimizing noxious emissions.
During a cold start engine condition, however, insufficient fuel vaporization, at least where a liquid fuel such as gasoline or diesel fuel is used, occurs if the multi-point injectors are used to provide fuel to the engine. The introduction of unvaporized or only partially vaporized fuel results in high fuel consumption, increased noxious emissions from the engine, as well as poor engine performance and slow starting. For that reason, many previously known internal combustion engines utilize a cold start fuel injector to provide vaporized fuel to the engine during a cold engine condition.
These previously known cold start fuel injectors introduce a sufficient vaporized fuel/air mixture into the intake of the primary intake manifold to provide the fuel charge for the combustion chambers of the engine during the engine warm up period. Where the internal combustion engine utilizes liquid fuel, many of these previously known cold start fuel injectors include heaters to enhance the vaporization of the fuel prior to its introduction to the engine combustion chambers. Such vaporized fuel minimizes noxious emissions and fuel consumption while not adversely affecting engine operation.
As the engine warms up, the cold start fuel injector is gradually deactivated while, simultaneously, the multi-point fuel injectors are gradually activated in order to provide a smooth transition between a cold engine condition and a warm engine condition.
Even though the heaters used by these previously known cold start fuel injectors have proven adequate for vaporizing liquid fuel, it is been the prior practice to introduce the vaporized fuel into the inlet end of the primary intake manifold. However, since the air/fuel mixture from the cold start fuel injector must pass through the still cold primary intake manifold of the engine, fuel condensation can occur within the intake manifold during a cold engine condition. Such fuel condensation adversely affects the efficiency of the engine and increases noxious emissions from the engine.
Furthermore, since the air/fuel mixture from the cold start fuel injector must travel entirely through the relatively large volume primary intake manifold before the air/fuel mixture reaches the internal combustion chambers, an appreciable time delay occurs between the activation of the cold start fuel injector and the time that the air/fuel mixture actually reaches the engine combustion chambers. This time delay may extend for several revolutions of the engine main shaft thus resulting in excessive engine cranking as well as slow engine starting.